1. Field of the Invention
The present invention relates to a gateway between networks each using a different communications protocol, and more particularly, to a gateway for connecting an asynchronous transfer mode (ATM)-based access network to an existing circuit public network.
2. Description of the Related Art
The Internet is providing an ever-increasing variety of useful information communication services. However, communication networks have been developing relatively slowly, so that access to the information services has been provided less quickly than expected. In order to solve this problem, establishment of an access network and a high-speed basic network are urgently required. Fortunately, high-speed information communication will be realized sooner or later because of technical developments related to digital subscriber line (hereinafter, called xDSL) technology, cable modems, high-speed wireless networks, satellites, etc. In the term xDSL, when x is A, the A denotes "asymmetric", and when x is V, the V denotes "very high speed".
However, a connection between this high-speed basic network or access network and an existing network (e.g., an existing packet network, a PSTN, an ISDN, etc.) has not yet been sufficiently studied.
Referring to FIG. 1, a connection of a conventional ATM network 100 to an existing circuit network 110 is performed in an ATM network exchanger. That is, the ATM network exchanger converts a protocol between networks using a specially-installed gateway, so that the ATM network 100 is connected to an existing packet network. Also, internally or externally installed in the ATM network exchanger is a device for emulating a circuit using an ATM adaptive layer (AAL-1) to connect the ATM network 100 to the existing circuit network 110. In FIG. 1, NSP denotes a network service provider, LT denotes line termination, NT denotes network termination, UNI denotes a user network interface, and ANI denotes an access network interface.
The above-described conventional connection is suitable when the number of subscribers connected to the ATM network is small. However, an increase in the number of subscribers due to the spread of the access network in the near future may overload protocol conversion to be made by a gateway unit. Also, when all the existing telephone network subscribers connect at once to the circuit network via the ATM network, the ATM network exchanger is overloaded, which makes highspeed information communications impossible.